Regarding speaking in tongues, in the verse that says "when that which is perfect is come," what does the word "perfect" mean in the Greek?
"Love never fails. But whether there are prophecies, they will fail; whether there are tongues, they will cease; whether there is knowledge, it will vanish away. For we know in part and we prophesy in part. But when that which is perfect has come, then that which is in part will be done away" (I Corinthians 13:8-10).
The Greek word translated as "perfect" is the word teleion. It means something that is complete, perfect, whole, full-grown, ripe, mature, or adult. The word can be used in the nominative or accusative form, it refers to a single thing, and can refer to something that is either masculine or neuter. The fact that it is "that which is perfect" and not "he who is perfect" indicates that we are referring to a thing (neuter) and not a person.
The same word is used in James 1:25, "But he who looks into the perfect law of liberty and continues in it, and is not a forgetful hearer but a doer of the work, this one will be blessed in what he does." Interestingly, despite contentions elsewhere, this particular word is not used in connection with Christ, though it is used to describe mature Christians (I Corinthians 2:6; Ephesians 4:13; James 1:4).